1. Field of the Invention
This invention relates generally to multi-layer printed circuit boards and more particularly to multi-layer circuit boards which are especially adapted for use in devices for testing integrated circuit chips.
2. Background of the Invention
Following the production of integrated circuit chips, it is necessary to test the chips individually to determined if indeed the chips are satisfactorily manufactured without defects or if there are defects or failures within the chips. This requires the application of signals to all of the chip input terminals, the signals being preprogrammed or preselected to provide a certain pattern of testing of the various devices within the chip through each of the signal input ports. In the case of so called flip chip type integrated circuit chips, the input ports are located across the surface thereof and not around the edge as is generally the case of DIP wire bond type chip technology and the testing apparatus must be supplied which will provide signal inputs to all of the various input ports on the so called chip "footprint".
Devices have been developed which utilize various typed of buckling beam probes mounted on a support member and connected through some type of external signal generator and programmer. The chip testing device requires that wiring that is connected to the external source of the signals be wired through the circuit board which in turn makes contact with the buckling beam probe to provide the necessary signals. It is necessary for signals at various different levels in addition to ground level be applied to the various different inputs of the chip since the chip itself normally will have several different signal levels as inputs when it is in operation. The challenge is to provide a printed circuit board, sometimes referred to as a probe space transform, that will receive the various signal levels and then apply the various received signal levels to the chip, each signal level being applied to the proper input pad on a given chip. Indeed as many as five or more different voltage levels may be required on any given chip, and each voltage connection must be applied to all of the various pads requiring that connection but not to any others.
One of the difficulties encountered with a printed circuit board which serves as the space transform is to provide a board design and manufacturing technique which will allow the voltage to be accurately received from the external source of the signals and accurately applied to the desired chip input pad locations. There have been many different types of circuit board designs which can receive and transform signals. Representative of printed circuit boards or the like are shown in U.S. Pat. Nos. 2,816,273; 4,311,979. U.S. Pat. No. 4,027,935 shows generally how a buckling beam probe can be used to supply test signals to a dip.